Structural and physical consequences of downsizing to form nanopowders or nanoceramics are very important both from applicative and fundamental point of view. We will discuss, using ab‐initio‐based calculation and Landau theory the origins and the consequences on structural properties when synthesizing nano‐objects with BaTiO3 and SrTiO3 , and show how to use nanostructuration to optimize properties such as electrocaloric effects or energy storage. For instance calculations in BaTiO3 show the possibility to form new phases (fig.1) in which vortices of polarization compete with homogeneous polarization or in which (in nanotorus) homogeneous hypertoroidization of nanotori coexists with axialhomogeneous toroidization. In SrTiO3 a new low temperature ground state, evidenced by synchrotron and neutron diffraction is discussed within the Landau theory and compared with the situation in thin films and during pressure experiments. The crucial competition between particles shape anisotropy, surface tension and shear strain is analyzed. Inducing a specific core‐shell structure is therefore a new and easy way to tailor structural properties and to stabilize new phases that cannot exist in bulk material, just like film deposition on substrate.

We present accurate measurement of the VV- and VH-polarized Raman spectra of vitreous SiO2 pressurized in the range 0 – 8 GPa in argon or helium atmosphere by means of diamond anvil cell. A fine quantitative analysis of the behavior of the Raman modes in function of pressure is achieved with the help of an old central-force model by Sen and Thorpe describing the dynamics of covalently bonded networks. The model predicts the effect of changes in force constants and bond angles on the vibrational frequencies of the coupled SiO4 tetrahedral network. We show that the pressure shift of the Raman bands cannot be understood without encompassing the variations of both parameters. Investigating two different pressurizing fluids including He which is adsorbed into the silica network, allows revealing the role of each parameter in the compression mechanism of the glass.

In this talk, some straightforward ways to obtain information from small-angle scattering on the structure of complex systems, in particular nanocomposites, will be given [1]. Polymer nanocomposites are mixtures of nanoparticles and polymer chains, where the particles – called filler – are usually added to enhance mechanical properties, like e.g. in car tires. Performances depend to a great extent on the structure of the filler, i.e. their dispersion state in the polymer matrix, which itself depends on mixing protocols, but also on the thermodynamics of the system. The latter can be tuned by performing either chemical surface modifications of the nanoparticles, or by playing with the mass and/or grafting properties of the polymer chains.We will present recent results on nanocomposites close to industrial applications, including what is probably one of the first quantitative analyses of such disordered structures by a combination of SAXS, TEM and numerical simulations [2]. The study led to the identification of a unique structure-determining parameter [3]. The generalization of the above-mentioned approach – the correlation hole analysis – will furthermore be illustrated by structural studies by small angle scattering of well-defined model systems, showing the influence of chain mass [4] or surface grafting of small molecules [5]. Finally, if the chairman is nice, a quick outlook on why contrast-matching with SANS in nanocomposites often fails will be proposed [6].[1] A.-C. Genix and J. Oberdisse, Structure and dynamics of polymer nanocomposites studied by X-ray and neutron scattering techniques. Current Opinion in Colloid & Interface Science, 2015, 20, 293-303.[2] G. P. Baeza, A. C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty and J. Oberdisse, Macromolecules, 2013, 46, 317-329.[3] G. P. Baeza, A.-C. Genix, C. Degrandcourt, J. Gummel, A. Mujtaba, K. Saalwächter, T. Thurn-Albrecht, M. Couty, and J. Oberdisse, ACS MacroLetters, 2014, 3 (5), 448–452[4] A. Banc, A. C. Genix, M. Chirat, C. Dupas, S. Caillol, M. Sztucki and J. Oberdisse, Macromolecules, 2014, 47, 3219–3230.[5] C. Schmitt Pauly, A.-C. Genix, J. G. Alauzun, M. Sztucki, P. H. Mutin and J. Oberdisse, Polymer, in press.[6] A. Banc, A.-C. Genix, C. Dupas, M. Sztucki, R. Schweins, M.-S. Appavou, J. Oberdisse, Macromolecules 2015, 48, 6596−6605.

High-pressure polarized Raman spectra of vitreous silica are measured up to 8 GPa in a diamond-anvil cell at room temperature. The combined use of either a nonpenetrating pressurizing medium—argon—or a penetrating one—helium, allows one to separate density from stress effects on the Raman frequencies. In the framework of a simple central force model, the results emphasize the distinct role played by the shrinkage of the intertetrahedral angle Si-O-Si and the force-constant stiffening during the compression. The polarization analysis further reveals the existence of an additional isotropic component in the high-frequency wing of the boson peak. The pressure dependence of the genuine boson peak frequency is found to be much weaker than previously reported and even goes through a minimum around 2 GPa in remarkable coincidence with the anomalous compressibility maximum of silica.